The present invention relates to stitching or stapling machines of the type which drive the legs of a generally U-shaped staple through an associated workpiece and against a clinching mechanism, which folds the legs up against the exit side of the workpiece. In particular, the present invention relates to the clinching mechanism for such a stitching or stapling machine.
This invention is an improvement of the wire stitching machine sold by Interlake, Inc., the assignee of the present invention, under the trademark "CHAMPION STITCHER". That prior stitching machine, which is in turn an improvement of the machine described in U.S. Pat. No. 1,252,011, includes a stitching head having a wire feed mechanism for feeding a predetermined length of wire from the continuous wire supply to a wire holder, where the length of wire is severed from the supply, and a staple-forming and driving mechanism which forms the severed length of wire into a staple and drives it into an associated workpiece. While the invention is designed particularly for use with that prior type of continuous wire stitching head, the principles of the present invention also have application to stitching machines of the type which drive preformed staples which may be fed, for example, from a magazine containing a supply of such staples.
One common type of clinching mechanism used with either the continuous wire or pre-formed staple type of stitching machine, is an in-line arrangement wherein the staple legs in their clinched condition are substantially coplanar with the bight portion of the staple. This arrangement is satisfactory where the workpiece thickness is fixed. But when the thickness of the workpiece can vary over a fairly wide range, the in-line arrangement will result in the staple legs interfering with each other when very thin work is being stapled. This problem can be avoided in the continuous wire stitching machines by adjusting them to vary the length of the staple cut from the continuous wire. But this adjustment is not a simple one, and is suitable only for applications involving fairly long runs at a given thickness and is inconvenient where frequent thickness changes are required.
For this latter condition, a different type of clinching arrangement known as bypass clinching is utilized, wherein the staple legs in their clinched condition are inclined with respect to the plane of the bight portion of the staple and are arranged to overlap or "bypass" each other. The length of the overlap varies as the workpiece thickness varies and, because the staple legs are not in line, they cannot interfere with each other in the clinched condition.
Prior bypass clinchers have utilized a pair of aligned clincher members, each having an angled groove or channel to respectively receive and guide the staple legs. These clincher members have recesses formed on their facing surfaces to accommodate the overlapping portion of the other staple leg. On occasion, particularly when thicker work is being stapled, the staple legs can sometimes stray or wander so that the point of exit from the work will not be in alignment with the point of entry. This can cause the leg to stray into the recessed portion of the associated clincher member, with the result that the leg will not be clinched and will remain in a vertical position.